1. Field of the Invention
The invention relates to transistorized, high speed, high voltage, high peak current switching circuits and in particular to such switching circuits when required to operate into a capacitive load.
2. Description of the Prior Art
Prior art switching devices have been primarily concerned with achieving high speed, high voltage switching while protecting the transistor switching elements from voltage breakdown. Gindi, in U.S. Pat. No. 3,007,061, teaches that low voltage transistors may be connected in cascade so as to hold off much higher voltages than the individual transistors themselves would be able to withstand.
When the switch must operate into a capacitive load the demands made upon the power supply may be great, if rapid charge of the load is required. At the first instant of charge-current flow, the load appears to the power source as a short circuit. Any resistance placed in the charging path to reduce the burden upon the power supply will increase the RC time constant of the charge path, thereby adversely affecting the time required for the load to reach full charge.
Although the average current requirements may be small, the ability to respond to peak current demands, where rapid charge of a capacitive load is necessary, often place an economic burden upon a system with respect to the specification of the power supply to be used in that system.
Picillo presents a switching circuit in U.S. Pat. No. 3,588,538 useful to rapidly discharge a capacitive load, but is not concerned with the speed at which the load is charged.
Shulka in U.S. Pat. No. 3,735,153 charges and discharges a peizoelectric crystal through current limiting charge and discharge resistors, 18 and 22 respectively. His primary objective was to provide timing control means in the base circuit of each transistor element for sequentially turning on or turning off the circuit.
Neither Picillo nor Shulka addressed a requirement for rapid charge of the load.
It shall be an object of the present invention to provide a high speed, high voltage switch capable of both rapidly charging and discharging a capacitive load.
It shall be a further object of the invention to provide a high speed charging circuit which makes minimal demands on the power supply.
Other objectives such as the provision for a simple, low power, TTL drive for transistor switch operation and transient protection of transistor switch elements will be made apparent as the invention is fully described.